Among the ceramics materials, calcium phosphate-based ceramics material is a main component of bone and tooth, has superior biocompatibility, and is superior in the safety. Therefore, it is widely utilized and studied as a biomaterial such as a medical or dental implant material to be implanted in the living body such as artificial bone, artificial dental root and the like, scaffold for cell culture to be used for regenerative medicine and the like, a drug carrier for drug delivery system (DDS) and the like.
Among these, the research and development are particularly actively performed in recent years of ceramics materials suitable for an artificial bone used for repairing or healing by filling in a defect or hole made in the bone due to a disease such as bone fracture, bone tumor and the like or a treatment thereof. Although ceramics materials are already used widely in the clinical practice, current ceramics materials are defective in that the new bone formation after implantation into an affected part is limited to the surface layer of the material and the strength is not sufficient, thereby prolonging the time necessary for healing the injury.
Accordingly, the development of a ceramics implant material, scaffold for cell culture and the like, which allow a biological tissue to rapidly penetrate into the inside and quickly form a tissue (new bone), and has a practical strength, is desired.
As such ceramics implant material, (1) calcium phosphate-based sintered body wherein many pores are densely distributed three-dimensionally, and a skeleton wall compartmentalizing adjacent pores has linked sphere-like opened pores communicating with them (see patent document 1), (2) a method of forming bead-shaped porous ceramics materials having pores by connecting them with a nylon wire and the like (see patent document 2) and the like are suggested.
Moreover, it is disclosed that a sintered body having unidirectionally-oriented penetrating pores with a diameter of 10-500 μm is a ceramics material suitable as an implant material (see patent documents 3, 4).
On the other hand, a method of obtaining various structures such as honeycomb-shaped structure, fiber-like structure and the like is known, which comprises descending and immersing a sol comprising water or a subliming substance such as tert-butyl alcohol and the like as a medium into a cooling medium, thus allowing the crystal of the medium to unidirectionally freeze, obtaining a frozen body by the use of the crystal as a template, and removing the medium (see patent document 5 and non-patent documents 1-3).    patent document 1: JP-B-3470759    patent document 2: JP-A-2003-335574    patent document 3: JP-A-2004-275202    patent document 4: JP-A-2005-1943    patent document 5: JP-A-2004-307294    non-patent document 1: The Yogyo Kyokai shi (Journal of the Ceramics Association, Japan) vol. 93 (7), 1985, p. 387    non-patent document 2: Carbon vol. 43, 2005, p. 1563    non-patent document 3: Carbon vol. 37, 1999, p. 2049